The present invention relates to a self-emulsifiable silicone composition or, more particularly, to an organopolysiloxane composition capable of being emulsified without use of any emulsifying agent to give a stable aqueous emulsion which is useful as an antifoam agent.
As is known, some of the antifoam agents based on a silicone or an organopolysiloxane are prepared of a block copolymer of an organopolysiloxane moiety and a polyoxyalkylene moiety as the main ingredient by utilizing the water-solubility and physical and chemical stability thereof. Such a block copolymer is useful also, in addition to the use as a base ingredient of silicon antifoam agents, as a mold release agent, fiber treatment agent, additive in cosmetics and toiletry preparations, foam-conditioning agent in the preparation of polyurethane foams and the like.
When the organopolysiloxane-polyoxyalkylene block copolymers are used as a principal ingredient of an antifoam agent of the aqueous emulsion type, however, the defoaming activity thereof can be exhibited only at a temperature higher than the clouding point thereof and the defoaming power is not quite satisfactory at a relatively low temperature around room temperature in comparison with other conventional linear diorganopolysiloxanes. Further, such a block copolymer is rather inferior to conventional diorganopolysiloxanes in respects of the mold releasability, water repellency and glossing effect in respective applications above mentioned.
Improved antifoam compositions suitable for defoaming in an aqueous dyeing solution for high-temperature dyeing of fabrics and aqueous cutting oils are prepared on the base of an organopolysiloxane-polyoxyalkylene block copolymer which is combined with a diorganopolysiloxane with or without further admixture of a silica filler and/or an organopolysiloxane resin as the principal ingredient of the antifoam composition. A problem in such an antifoam agent prepared of a diorganopolysiloxane and a block copolymer of the above mentioned type in combination is the contradictory requirements for the stability of the aqueous emulsion and the effectiveness of the defoaming activity. That is, the defoaming activity can be enhanced by increasing the relative amount of the diorganopolysiloxane to the block copolymer while such an emulsion composition of high diorganopolysiloxane content is disadvantageous in the poor emulsifiability as well as in the mechanical stability and storability of the prepared emulsion. When the proportion of the block copolymer is increased, on the other hand, the emulsifiability and the stability of the emulsion can be improved though with sacrifice of the defoaming activity, especially, at low temperatures, e.g. room temperature.